Heretofore, an electrostatic induction conversion device such as a power-generating unit or a microphone has been proposed wherein an electret having an electric charge injected to an insulating material, is used.
As the insulating material for such an electret, it has been common to use a linear fluororesin such as polytetrafluoroethylene.
Recently, it has been proposed to use a polymer having a fluorinated alicyclic structure in its main chain (e.g. Patent Document 1), as the insulating material for such an electret. Further, it has also been proposed to improve the surface voltage by using one having a silane coupling agent further mixed to a polymer having a fluorinated alicyclic structure in its main chain and having a carboxy group as its terminal group, as the insulating material for an electret (Patent Document 2). Patent Document 2 discloses an Example wherein a polymer having an intrinsic viscosity of 0.23 (corresponding to a weight average molecular weight of 165,000) and a silane coupling agent are mixed and thermally treated at 200° C.